opencode-thinking-fix

npm install opencode-thinking-fix

Fix for the reasoning_content 400 error that kills multi-turn conversations with DeepSeek, Kimi, GLM, and MiMo in OpenCode.

Table of Contents

• What problem this fixes
• Option 1: Plugin (stops the crashes)
• Option 2: Proxy (replays real reasoning)
• Option 3: Watchdog (auto-recovery)
• How they work together
• Affected models
• Model routing
• Is it working?
• Running tests
• This bug is everywhere
• Files in this repo

What problem this fixes

You ask DeepSeek a question. It picks a tool, calls it, works fine. Then you ask a follow-up and you get this:

HTTP 400: The reasoning_content in the thinking mode must be passed back to the API

DeepSeek V4 (and Kimi K2.7, GLM 5.x, MiMo V2.5) require that reasoning_content from every prior assistant turn gets included in subsequent API requests. The docs say it clearly: if you do not pass back reasoning_content correctly, the API returns a 400 error.

OpenCode's provider layer drops this field. Three upstream PRs (#24250, #24428, #24895) tried to fix it. None merged. The field is non-standard per OpenAI, so both OpenCode and the AI SDK ignore it.

This repo fixes it. Three layers, pick what you need.

Option 1: plugin (stops the crashes)

One file. Drop it in ~/.config/opencode/plugins/ and restart:

mkdir -p ~/.config/opencode/plugins
cp plugins/opencode-thinking-fix-universal.ts ~/.config/opencode/plugins/

It scans outgoing messages for any assistant turn that already has reasoning_content. If it finds one (meaning you are using a reasoning model), it adds reasoning_content: "" to every assistant turn missing it. If it finds nothing (Qwen, GPT, Claude — they never produce this field), it does nothing.

It also handles reasoning for the OpenCode Go provider, and patches empty content fields that OpenAI-compatible SDKs sometimes omit.

No config file changes. No build step. OpenCode compiles .ts plugins when it starts.

The catch: the plugin fills in empty strings, not your model's actual prior thinking. DeepSeek, Kimi K2.5/K2.6, GLM, and MiMo accept empty strings fine — your conversation works but the model does not see its earlier reasoning. Kimi K2.7 Code rejects empty strings entirely, it needs the real text.

Option 2: proxy (replays real reasoning)

A Node.js proxy that catches API responses as they come back, pulls out the actual reasoning_content text, and caches it in memory. On the next request, it injects that real text back into the conversation history instead of empty strings.

Your model sees its full chain-of-thought from turn 1 on every subsequent turn. The difference is noticeable on complex multi-turn coding sessions.

Two-proxy architecture

The proxy runs on two ports:

Port 3457 auto-routes based on model name using the built-in route table. Port 3458 is a fixed-upstream proxy specifically for the OpenCode Go provider, which uses delta.reasoning (not reasoning_content) in its SSE streams. Both are handled by the same proxy.js binary — just different environment variables.

# run port 3457 (direct providers)
node proxy/proxy.js

# run port 3458 (OpenCode Go)
PORT=3458 UPSTREAM_URL=https://opencode.ai/zen/go/v1 node proxy/proxy.js

Install as systemd services (auto-start at boot)

mkdir -p ~/.config/systemd/user
cp systemd/reasoning-cache.service ~/.config/systemd/user/
cp systemd/reasoning-cache-go.service ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now reasoning-cache.service
systemctl --user enable --now reasoning-cache-go.service

Then point OpenCode at it — in your opencode.json:

{
  "provider": {
    "deepseek-v4-pro": {
      "baseURL": "http://127.0.0.1:3457/v1"
    },
    "opencode-go": {
      "baseURL": "http://127.0.0.1:3458/v1"
    }
  }
}

Zero npm dependencies. It uses http, https, and url — nothing else.

Kimi K2.7 Code and OpenCode Go need this. The rest of the models benefit from it but do not technically require it.

Option 3: watchdog (auto-recovery)

The watchdog script checks both proxy instances every 4 minutes and restarts any that are down:

cp watchdog/watchdog.sh ~/reasoning-cache-proxy/
cp systemd/reasoning-proxy-watchdog.service ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now reasoning-proxy-watchdog.service

How they work together

OpenCode → [plugin patches missing reasoning_content/reasoning]
         → [proxy injects cached real text]
         → [watchdog keeps both proxies alive]
         → API

The plugin is the safety net. If the proxy goes down, the plugin still injects empty strings so you do not get 400s. If the proxy is up, its cached text takes priority because the plugin sees the field is already filled in. Either way, your conversation does not break.

Affected models

Model routing (proxy port 3457)

The proxy auto-routes by model name prefix. All 15 supported prefixes:

Unknown models fall back to https://api.deepseek.com with reasoning disabled.

Is it working?

Turn 1 will not show anything — there is no history to patch yet. That is normal.

Turn 2+, check the console:

Plugin working:

[ThinkingFix] patched 3 field(s) across 11 message(s)

Proxy working:

[Cache] session abcdefgh: stored reasoning turn 0 (1842 chars)
[Cache] session abcdefgh: replayed reasoning for turn 0 (1842 chars)

If nothing shows up, either it is a non-reasoning model (correct) or the plugin did not load (check for [ThinkingFix] Plugin loaded at startup).

Quick proxy health check:

curl http://127.0.0.1:3457/health
# → {"ok":true,"uptime":42}
curl http://127.0.0.1:3458/health
# → {"ok":true,"uptime":42}

Proxy logs:

journalctl --user -u reasoning-cache.service -f
journalctl --user -u reasoning-cache-go.service -f

Running tests

npm test
# or directly:
node tests/test-plugin.js
node tests/test-proxy.js

The plugin tests cover 12 cases: native reasoning model detection, OpenCode Go reasoning field detection, non-reasoning model passthrough, mixed messages, multiple assistant turns, already-complete messages, wrapper format ({ info: Message }), empty reasoning_content, empty arrays, tool_calls with reasoning and without, and null/undefined wrappers.

The proxy tests cover 15 cases: route resolution for all model prefixes, patchRequestBody injection from cache for both reasoning_content and reasoning, no-cache fallback to empty strings, user message isolation, multi-turn caching, and SSE stream parsing for delta.reasoning_content, delta.reasoning, content-triggered flush, and finish_reason flush.

This bug is everywhere

OpenCode is not the only tool that drops reasoning_content. Here is a partial list of places this same bug shows up:

OpenCode (anomalyco/opencode): #24190, #24104, #24722, #25311, #25134, #25000, #24124, #24130, #24261, #24442, #24569

OpenClaw: #71435, #71050

Kilo Code: #9501

VS Code: #318920

OpenAI Codex: #24500

GitHub Copilot: discussion #193953

OmniRoute: #1628

Reddit: r/opencodeCLI, r/DeepSeek, r/RooCode

Blogs covering it: AkitaOnRails, ClawHub

Files in this repo

plugins/
  opencode-thinking-fix-universal.ts   # self-detection plugin (106 lines)
proxy/
  proxy.js                              # reasoning cache proxy (333 lines, zero deps)
tests/
  test-plugin.js                        # plugin unit tests (228 lines, 12 cases)
  test-proxy.js                         # proxy unit tests (359 lines, 15 cases)
watchdog/
  watchdog.sh                           # auto-recovery watchdog (64 lines)
systemd/
  reasoning-cache.service               # proxy systemd unit (port 3457)
  reasoning-cache-go.service            # OpenCode Go proxy unit (port 3458)
  reasoning-proxy-watchdog.service      # watchdog systemd unit

Tested on

OpenCode v1.17.9, Kubuntu 24.04, DeepSeek V4 Pro, OpenCode Go.